1) Field of the Invention
The present invention relates to an illuminating apparatus, an image display apparatus, and a projector, and more particularly, to an illuminating apparatus for a projector.
2) Description of the Related Art
Generally, light emitting diode (LED) has an advantage of a long lifetime and a high energy-conversion-efficiency over an ultrahigh-pressure mercury vapor lamp. For this reason, the LED is gaining popularity as light source for an illuminating apparatus. However, a single LED has a smaller emission amount compared to the ultrahigh-pressure mercury vapor lamp. Because a comparatively large amount of light is required for a projector, a technology for making an array of LEDs is proposed in, for example, Japanese Patent Application Laid-Open Publication No. 2001-305657 to achieve a sufficient light intensity.
When a plurality of LEDs is arrayed, the light intensity increases proportional to the number of LEDs. In a projector, it is possible to express a spatial extent, where an effective light flux exists, as a product of dimension and solid angle (etendue, geometrical extent) in an optical system including light source and a spatial light modulator. The product of dimension and solid angle is preserved in the optical system. Hence, if the spatial extent of the light source becomes larger, the spatial extent where the light flux incident on the spatial light modulator becomes larger. However, because an angle that the spatial light modulator can cover is limited, it is difficult to effectively use the light flux from the light source. When a plurality of LEDs is arrayed to increase the light intensity, the dimension of the light source (spatial extent) also increases. Therefore, even if an LED array is employed in a projector to increase the light intensity, it is difficult to effectively use all the light flux from the light source because the etendue is preserved.
In a so-called single-LCD-panel projector that employs a single liquid-crystal spatial-light-modulator, a red light (R-light), a green light (G-light), and a blue light (B-light) are illuminated to corresponding pixels, respectively. The single LCD panel projector has an advantage of a simple and compact configuration over a so-called triple-LCD-panel projector that employs a spatial light modulator for each of color lights. The single LCD panel projector that displays a full color image using a single liquid-crystal spatial-light-modulator can be configured by preparing a pixel for the R-light, a pixel for the G-light, and a pixel for the B-light and illuminating the R-light, the G-light, and the B-light to the pixels corresponding each of the colors, respectively, as proposed in, for example, Japanese Patent No. 2622185.
According to the configuration disclosed in the Japanese Patent No. 2622185, a white light from light source is separated into the R-light, the G-light, and the B-light by color filters that selectively transmit and reflect the R-light, the G-light, and the B-light, respectively. A microlens is disposed for each of three pixels, the pixel for the R-light, the pixel for the G-light, and the pixel for the B-light. Lights passing through the color filters for each of the color lights have different angles, respectively, by which the R-light separated by the color filter is incident on a corresponding pixel for the R-light. Furthermore, the G-light separated by the color filter is incident on a corresponding pixel for the G-light, and the B-light separated by the color filter is incident on a corresponding pixel for the B-light. In this manner, the R-light, the G-light, and the B-light are expressed with three pixels. With this type of configuration, because the white light is separated into three colors by the color filters for each of the colors, an illumination optical system grows in size, and it is difficult to obtain a bright image with an even intensity distribution. As described above, the conventional technology has problems of supplying an illumination light with a high brightness and a high usability and obtaining a bright image with an even intensity distribution.